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Advances in the aquatic sciences
RESEARCH FRONT

Effects of shading on seagrass morphology and thermal optimal of productivity

Eunice Kong A B E , Yan Xiang Ow https://orcid.org/0000-0003-4659-4951 C , Samantha Lai A , Siti Maryam Yaakub D and Peter Todd A
+ Author Affiliations
- Author Affiliations

A Experimental Marine Ecology Laboratory, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Block S3, Level 2, Singapore 117543, Republic of Singapore.

B National Biodiversity Centre, National Parks Board, 1B Cluny Road, Singapore 259569, Republic of Singapore.

C St John’s Island National Marine Laboratory, Tropical Marine Science Institute, National University of Singapore, 18 Kent Ridge Road, Singapore 119227, Republic of Singapore.

D DHI Water & Environment (S) Pte Ltd, 2 Venture Drive, #18–18, Vision Exchange, Singapore 608526, Republic of Singapore.

E Corresponding author. Email: eunicekong@hotmail.sg

Marine and Freshwater Research 71(8) 913-921 https://doi.org/10.1071/MF19173
Submitted: 15 May 2019  Accepted: 13 September 2019   Published: 6 December 2019

Abstract

Light and temperature are important factors affecting seagrass primary productivity. Acclimatisation to reduced light availability may affect the optimal temperature at which seagrasses photosynthesise, potentially causing synergistic effects between increasing water temperatures and decreasing light levels on coastal productivity. This study investigated the effects of reduced light availability on the morphology (leaf size, shoot density) and thermal optimal of net productivity in Halophila ovalis (R.Br.) Hook. A 12-week in situ shading experiment was conducted at Chek Jawa Wetlands, Singapore, testing high (68% shading), low (49%) and control (0%) shadings. Every 4 weeks, photosynthetic and respiration rates of H. ovalis leaves and the root–rhizome complex were measured in closed incubation chambers at temperatures from 22 to 42°C (at 4°C intervals). A fitted temperature-response model of net photosynthesis was used to estimate the thermal optimal for each shading treatment. High shading reduced shoot density (mean ± s.e.) 87.06 ± 7.86% and leaf surface area 31.72 ± 24.74%. Net productivity (6 mg O2 g–1 DW h–1) and its thermal optimal (28–30°C) were not significantly different among shading treatments throughout the experiment. Light levels appeared to have minimal influence on the thermal dependency of H. ovalis net productivity.

Additional keywords: Halophila ovalis, light limitation, net primary productivity, optimal temperature, Singapore, tropical seagrass.


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